1. Field of the Disclosure
The disclosure relates to preassembled ferruled connector assemblies and connectors, including multi-fiber connector assemblies and connectors, and particularly to mechanical referencing of ferrules configured for preassembled connector assemblies during optical fiber polishing and measurement and methods therefor.
2. Technical Background
Optical fibers are used for a variety of applications including voice communications, data transmission and the like. In this regard, FIG. 1 schematically illustrates two preconnectorized fiber optic cables 10 and 10′ being routed to a premises 12 of a subscriber using two different exemplary installation techniques. Specifically, FIG. 1 shows a first preconnectorized fiber optic cable 10 being routed to the premises 12 in an aerial installation and a second preconnectorized fiber optic cable 10′ being routed to the premises 12 in a buried installation. In the aerial installation, a first end 10A of the preconnectorized cable 10 is attached at a first interface device 14 located at, or near, a pole 16. A second end 10B of the preconnectorized cable 10 is attached at a second interface device 18 located at the premises 12. By way of example, the first interface device 14 may be a closure, multiport (a device having multiple receptacles), or the like, and the second interface device 18 may be a closure, network interface device (NID), optical network terminal (ONT), or the like. In a buried installation, a first end 10A′ of the preconnectorized cable 10′ is attached at a first interface device 20, which is typically disposed in a housing 22. A second end 10B′ of the preconnectorized cable 10′ is attached at the second interface device 18 located at the premises 12.
In order to interconnect a plurality of optical fibers with a minimum amount of attenuation, a pair of multi-fiber connectors is preferably mated such that the opposing optical fibers are biased into contact with one another. To achieve optimal transmission without utilizing refractive index matching gel, the multi-fiber connectors must be precisely aligned in order to correspondingly align the individual optical fibers in the connectors. This alignment is typically provided by guide pins that extend outwardly from the end face of a male multi-fiber ferrule for insertion into corresponding guide pin openings, grooves or other structures defined by a female multi-fiber ferrule. In addition for precise alignment, the geometry of the ferrule and, in particular, the polish geometry of the end face of the ferrule, is extremely important to insure proper fiber-to-fiber contact.
In this regard, at least the portion of the end face of each ferrule that is proximate to the optical fibers is preferably polished to define a plane extending perpendicular (or angled to) to the longitudinal axis defined by the guide pin openings and, therefore, perpendicular to the fiber bores. In addition, the planar surface defined by the portion of the end face of each ferrule proximate to the fiber bores is precisely positioned relative to the ends of the optical fibers. For example, with proper polish geometry, the optical fibers will extend by a predetermined distance beyond the end face of the ferrule so that fiber-to-fiber contact between opposing optical fibers is established. If, however, the polish geometry is not precisely defined, fiber-to-fiber contact may be prevented or otherwise obstructed by contact between those portions of the end faces of the opposing ferrules that extend beyond the ends of the optical fibers.
In order to monitor the polish geometry and the resulting quality of each ferrule, it is desirable to determine the planarity of the end face of the ferrule and the angle of the end face relative to the guide pin openings. As such, FIGS. 2A and 2B illustrate a ferrule 30 in which an end face reference surface 32, also referred to herein as the “region of interest,” is measured for planarity. The end face reference surface 32 is an area on the end face 34 of the ferrule 30 in the vicinity of a plurality of fiber bores 36. Truncated measurement pins 38A, 38B having very precisely machined ends that extend from the end face 34 of the ferrule 30 can be used to determine if the end face reference surface 32 of the ferrule 30 has been properly molded or machined to be planar. In order to determine the planarity of the end face reference surface 32, the measurement pins 38A, 38B are inserted into guide pin openings 40A, 40B, respectively, to define measurement pin reference surfaces 42A, 42B.
Referring to FIG. 2B, the measurement pins 38A, 38B are machined to be very flat on one of their reference surfaces 42A, 42B. The plane defined by the measurement pin reference surfaces 42A, 42B of one or both of the measurement pins 38A, 38B can then compared to the end face reference surface 32 using an interference vision system, such as an interferometer having three dimension (3D) capabilities. After comparative measurements have been made and the planarity of the end face reference surface 32 confirmed, the measurement pins 38A, 38B are removed from the guide pin openings 40A, 40B and replaced with conventional guide pins to produce a male ferrule. A female ferrule is produced with vacant guide pin openings 40A, 40B operable for receiving the guide pins of a respective male ferrule. Predetermined lengths of optical cable may then be produced by combining sections of cable comprising mating male and female ferrules.
There are several disadvantages associated with using truncated measurement pins 38A, 38B to measure the planarity of the end face reference feature 32 and/or the angularity of the end face 34. For one, the measurement pins 38A, 38B are expensive to manufacture because of the very precise machining of one of their ends. Furthermore, the measurement pins 38A, 38B may be easily lost due to their extremely small size. Also, when using the ends of the measurement pins 38A, 38B as a reference surface, it is necessary to make the optical measurements using a relatively expensive interference vision system having 3D capabilities. Still further, with conventional multi-fiber ferrules, male multi-fiber ferrules cannot be measured for planarity after assembly due to the difficulty in removing the guide pins without possibly damaging the ferrule assembly. Consequently, there is an unresolved need in the art for a simpler, faster, and less expensive way to make planarity measurements.